In this study, the stiffness and the strength of spatially reinforced composites (SRC) are predicted by using superposition of a rod and matrix stiffnesses in an arbitrary direction. To confirm the predicted values, the material properties of SRC are measured. The predicted values from the volume average of stiffness matrix are consistent with the tested values in a rod direction, but are inconsistent in an off-rod direction while reverse is true for the volume average of compliance matrix. Therefore, the harmony function from superposition of stiffness and compliance matrix is introduced. The predicted values from the harmony function are consistent with the tested values in both the rod and the off-rod directions. Studied are the elastic behavior, temperature distribution, and thermo-elastic behavior of a kick motor nozzle composed of carbon/carbon SRC as a throat part. The elastic deformation of the nozzle composed of 3D carbon/carbon SRC shows asymmetry in a circumferential direction. However, 4D carbon/carbon SRC nozzle shows uniform deformation in the circumferential direction. Stress concentration in connecting parts of the kick motor nozzle is ultimately high due to the high temperature gradient in each connecting part. The thermo-elastic deformations of both the 3D and the 4D SRC nozzles are uniform in the circumferential direction due to the isotropy of CTE of each SRC. The deformation of the 3D SRC nozzle is a slightly smaller than that of the 4D SRC nozzle in the nozzle throat, which is favorably effective on rocket thrust. The circumferential stress is the most critical component of the kick motor nozzle. The 4D SRC nozzle having 1,1,1,1.7 diameters in each direction has the smallest circumferential stress among several SRC nozzles.
